The present invention relates generally to medical devices and more particularly to introducer sheaths that are used for the transcutaneous introduction of catheters and other apparatus into a patient. The present invention relates more particularly to fittings on the proximal end of such introducer sheaths that permit the introducer sheath to be easily removed when no longer needed for the procedure.
Introducer sheaths are commonly used in various medical procedures where a catheter is transcutaneously introduced into an interior body lumen or cavity, such as a blood vessel or a hollow body organ. Typically, the introducer sheath comprises a thin-walled sheath tube that is introduced through a previously formed needle penetration. The introducer sheath can be introduced together with an internal stylet or obturator, where the stylet or obturator has a tapered distal end that extends from the sheath and dilates the previously formed hole as the sheath is advanced. After the combination of the sheath and stylet/obturator has been introduced, the stylet/obturator is removed, leaving a working channel defined by the axial lumen of the sheath. Catheters and other working devices can then be introduced through the working channel to perform various medical procedures.
Various improvements in the design of such introducer sheaths have been proposed. Of particular interest to the present invention, introducer sheaths have been designed where the sheath is weakened along opposed axial lines to facilitate splitting when the proximal end of the sheath is pulled apart. Splittable introducer sheaths can also be formed of materials, like poly-tetrafluoroethylene (TFE), having inherent molecular structure facilitating splitting of the sheath even in the absence of any structural weakening, as disclosed in U.S. Pat. No. Re31,885. Both forms of splittable sheaths are useful when it is desirable to remove the sheath from around a catheter or other device that is to remain in place in the transcutaneous penetration. In general, the proximal end of the sheath has a short longitudinal xe2x80x9cstarterxe2x80x9d slit that initiates the splitting or peeling action by which the sheath may split or pulled apart as it is withdrawn, thus facilitating its removal. Without the ability to peel away the sheath, it would be impossible to remove the sheath over any enlarged proximal hub or housing on the catheter or other device that is intended to remain in place. The short longitudinal xe2x80x9cstarterxe2x80x9d slits form a pair of flaps or tabs to which small knobs can be attached to facilitate the gripping of the tabs when the removal of the sheath is desired. In some prior art devices, such as are shown in U.S. Pat. Nos. 5,250,033; 5,098,392 and 4,596,559, the tabs have taken the form of a splittable T-shaped fitting molded onto the proximal end of the sheath. The combination of such prior art splittable T-shaped fittings molded together with sheaths formed of TFE has proven to be impossible due to the slickness of the TFE.
It has been suggested in U.S. Pat. No. 4,596,559 to form a splittable T-shaped fitting that mechanically engages the flaps or tabs at the proximal end of the sheath. The fitting includes pins that are intended to extend through holes in the flaps or tabs of the sheath. Hinged portions of the T-shaped fitting are intended to hinge over the tabs or flaps and engage the pins so that the tabs are captured between the hinged portions. However, the actual assembly of the structure disclosed in U.S. Pat. No. 4,596,559 is not possible without prematurely splitting the handle along the zone of reduced thickness, thus significantly reducing the structural integrity of the combined structure to the point that it is no longer serviceable in the intended manner.
The present invention is directed to a novel structure for a splittable T-shaped fitting that includes a mechanical capture of the sheath tabs while retaining all the structural integrity required to perform the desired functions including locking engagement with a dilator fitting. The present invention is particularly suitable for use with sheaths made of TFE or other slick materials, but can be used with sheaths made of any material. The present invention also includes a low stress engagement feature to engage a dilator fitting that includes a tactile report of engagement with the dilator fitting.
A splittable sheath assembly of the present invention includes a sheath, a T-shaped fitting and an attachment mechanism. The sheath is adapted for use in the transcutaneous insertion of medical instrumentation through a lumen defined by the sheath and has a distal end and a proximal end. The proximal end includes an initial bifurcated portion defining two tabs. The T-shaped fitting has a central opening aligned with the lumen of the sheath and a handle on either side of the central opening. A zone of weakness separates the two handles so that the T-shaped fitting is adapted to be split into two separate portions, each portion having only one of the handles. The attachment mechanism attaches each of the tabs of the proximal end of the sheath to one of the handles.
Each attachment mechanism includes a projection at least engaging a portion of one of the tabs. A locking element is received over the projection to inhibit movement of the tab relative to the projection. Each attachment mechanism is embedded in the T-shaped fitting so that each portion of the T-shaped fitting is coupled to only one of the sheath tabs. The attachment mechanisms can be encapsulated in the handles of the T-shaped fitting by insert molding the splittable handles around the attachment mechanisms using casting, injection molding or compression molding techniques. The polymers suitable for use as the T-shaped fitting include both thermoset and thermoplastic resins. The attachment mechanism is preferably formed as a unitary element including a hinge portion between a projection supporting portion and the locking element so that the locking element can be folded over on top of the projection-supporting portion so as to capture one of the tabs of the proximal end of the sheath. Materials suitable for use as the attachment mechanism include a wide variety of injection-moldable thermoplastic resins. Preferably the resins employed for the T-shaped fitting and the attachment mechanisms are selected to be compatible with each other during the embedding process.
The projecting portion can take the form of a peg suitable to be received in a preformed hole in the tab, or a pin suitable to puncture a hole in the tab. The projecting portion can also take the form of a series of teeth received in inter-dental spaces, ridges received in furrows, or other patterns of projections and corresponding recesses, the recesses being generally found on the coupling portion of the attachment mechanism. The projection can be suitably configured to engage the coupling portion. Alternatively, the coupling portion can be at least temporarily engaged by a separate locking flap so that the sheath tab can be retained in position during the insert molding process. Alternatively still, the coupling portion can be held in a clamping position relative to the sheath tabs by structural elements of the mold in which the insert molding process takes place.
The T-shaped fitting is preferably molded to include a snap feature adapted to receive a dilator fitting. The snap feature is defined by a pair of short ridges in the lumen of the T-shaped fitting, the pair of ridges being situated generally along the line of the zone of weakness between the two handles. This orientation for the ridges coupled with their short length minimizes the forces applied to the fitting, particularly in the direction that would cause the handles to separate, thus avoiding any premature splitting of the handles by any insertion of a dilator fitting into the lumen of the T-shaped fitting. The short ridges preferably located on opposite sides of the lumen from each other. The short ridges preferably occupy only about 30xc2x0 of arc around the inside of the lumen, and are skewed from the plane defined by the zone of weakness by only about 15xc2x0. A dilator hub designed for engagement with the short ridges of the T-shaped fitting includes a peripheral engagement ring situated on a forward portion of the hub that will preferably snap fit into place without placing undue strain on the T-shaped fitting. The snap fit allows for quick insertion by the physician and a tactile signal of engagement to the physician.
While certain features and advantages of the present invention has been identified generally in the forgoing discussion, additional features and advantages will become apparent to those skilled in the art from the following description of a preferred embodiment of the invention, which references the accompanying drawings and discloses the best mode of the invention as present perceived.